Apparatus for hydraulic crushing

ABSTRACT

The apparatus is for crushing samples in preparation for analysis. A support vessel receives and supports a comparatively thin walled sample container, which may be filled and sealed separately from the crushing apparatus. A clamp clamps the sample container in the support vessel and effects electrical connection between electrodes molded in situ in the sample container and plates connected across capacitors for providing high-voltage pulses. The thin walled sample container is disposable so that cross-contamination is avoided by using a new sample container for each sample to be crushed.

United States Patent [72] Inventors Joseph Dodman Wilson Oxford;

Bertram Reginald Donoghue, Didcot; John Lester Waddingham, Abingdon, allof,

England Appl. No. 7,853 Filed Feb. 2, 1970 Patented Sept. 14, 1971Assignee United Kingdom Atomic Energy Authority London, England PriorityFeb. 10, 1969 Great Britain 7 168/69 APPARATUS FOR HYDRAULIC CRUSHING 8Claims, 1 Drawing Fig.

US. Cl 241/301 Int. Cl 1302c 19/18 Field of Search 241/1 46,

[56] References Cited UNITED STATES PATENTS 3,208,674 9/1965 Bailey241/l 3,352,503 l1/1967 Maroudas... 24l/30l 3,529,776 9/1970 Meszaros241/301 X Primary ExaminerGranville Y. Custer, Jr. An0rneyLarson andTaylor ABSTRACT: The apparatus is for crushing samples in preparationfor analysis. A support vessel receives and supports a comparativelythin walled sample container, which may be filled and sealed separatelyfrom the crushing apparatus. A clamp clamps the sample container in thesupport vessel and effects electrical connection between electrodesmolded in situ in the sample container and plates connected acrosscapacitors for providing high-voltage pulses. The thin walled samplecontainer is disposable so that cross-contamination is avoided by usinga new sample container for each sample to be crushed.

APPARATUS FOR HYDRAULIC CRUSHING BACKGROUND OF THE INVENTION Theinvention relates to apparatus for electrohydraulic crushing of samplesfor analysis.

A spark discharge taking place in a liquid causes intense shock waves tobe set up in the liquid and, in electrohydraulic crushing, it is theseshock waves which are used for crushing materialin the liquid. Thetechnique is particularly useful .for crushing hard materials such ascarbides or oxides which are difficult to crush by conventionaltechniques.

The present invention is based upon the appreciation that by makingprovision for avoiding or controlling contamination, theelectrohydraulic crushing technique is particularly suitable forpreparing samples of material, difficult to crush by conventionaltechniques, for subsequent analysis.

SUMMARY OF THE INVENTION The invention provides apparatus forelectrohydraulic crushing of samples for analysis, which apparatuscomprises a support adapted to receive a separately formed samplecontainer having spaced electrodes therein, means for clamping thesample container in the support, and means for connecting the electrodesacross a high-voltage source.

It is an important feature of the invention that the apparatus isconstructed and arranged so that a sample container is supported overthe whole, or substantially the whole, of its outer surface, whereby thesample container is supported against the explosive forces ofelectrohydraulic crushing therewithin. The sample container may thus beconstructed of thin material such as may conveniently. be disposed ofafter use in crushing one sample. A new sample container may thereforebe used for each analysis and the possibility for cross-contaminationsignificantly reduced.

Preferably the support comprises a vessel, the internal shapeanddimensions of which correspond with the exterior shape and dimensionsofthe sample container. Preferably the clamping means includes a memberwhich overlies the lid of a sample container when positioned in thesupport, the arrangement being such that the clamping pressure whenapplied,

serves to press the lid of the sample-container into tightly sealedengagement with the sample container body.

Preferably the arrangement is such that the clamping meanssimultaneously serves to press the lid as aforesaid and to press intoelectrical contact with the electrodes electrical contact membersadapted for electrical connection to the high voltage source.

Preferably the high-voltage source provides'high-voltage pulses andcomprises one or more capacitors, means for charging the capacitors andmeans for intermittently discharging the capacitors through theelectrodes of a sample container clamped in the apparatus. Preferablythe means for intermittently discharging the capacitors comprises anair, or other gas, gap between further electrodes in series with theelectrodes of the samplecontainer. When thepotential across thecapacitors has built up to a predetermined level, the airgap breaks downand discharge through the sample container is initiated. When thecapacitors have discharged, arc discharge through the air gap ceases andrecharging commences.

The invention also provides apparatus for electrohydraulic crushing ofsamples for analysis comprising opposed rigidly supported electricallyconducting plates, one of which has an aperture therethrough, one ormorecapacitors disposed between the plates and electrically connectedacross the plates, a support vessel of electrically insulating materialreceived in the said aperture and having a flange overlying part of theplate, clamping means comprising a member adapted to overlie the lid ofa sample container supported in the support vessel, and means forpressing the clamping member towards the said apertured plate, anelectrical contact member provided in the support vessel andelectrically connected, preferably via a switchable means such as anairgap, to the other of the said plates, an electrical contact memberprovided in or by the clamping member, the arrangement being such thatwhen clamping pressure is applied with a sample container supported inthe support-vessel,the clamping member applies sealing pressure to thelid of the sample container and electrical contact making pressurebetween electrodes in the sample container and the respective electricalcontact members.

The invention includes a sample container for samples to beelectrohydraulically crushed prior to analysis, which containercomprises electrodes around which plastics material is molded,preferably injection molded, to form the container.

Specific constructions of apparatus for electrohydraulic crushingembodying the invention will now be described by way of example and withreference to the accompanying drawing, which is a diagrammatic sectionalview of the apparatus.

In the example shown in the drawing the apparatus is forelectrohydraulic crushing of small quantities of material for subsequentanalysis. The apparatus comprises two circular brass plates 11 and 12between which are arranged five capacitors in a ring. Two of thesecapacitors 13, 14 are visible in the drawing. Each of the capacitors hasa working voltage of 60 kv. and a capacity of 0.005 microfarads. Thecapacitors are mechanically secured between the plates 11 and 12 and areelectrically connected across these plates. The plate 11 forms anearthed plate and means is provided at 15 for connecting the plate 12 toan l-LT. supply through a charging resistor (not shown).

The plate 11 has a centrally located aperture in which is received asupport vessel 16. The support vessel 16 is cylindrical with an outsidediameter of 2 inches and has an annular flange 17, of outside diameter 3inches, for overlying the plate 1 l to locate and support the supportvessel 16 in the aperture in the plate 11. The overall length of thesupport vessel l6'is, in this example, 2 7/16 inches and the upper end(as seen in the drawing) has an internal bore 18 of diameter 1 H2 inchesextending 1 1/8 inches along the length of the support vessel 16. Thebore 18 tapers to a bore 19 of diameter 7/ l 6 inches. A bore 21 ofdiameter 5/ 16 inches extends from the bottom end (as seen in thedrawing) of the support vessel 16 into the bore 19, leaving an annularshoulder between the bores 19 and 21.

The support vessel 16 is formed from an acetyl based plasticsv materialsuch as Delrin (registered trade mark) by injectionmolding.

Extending out of the bore 21 in the support vessel 16 is -a brasselectrical contact member 22 which is retained by its head 23 engagingthe shoulder between the bores 19 and 21, The brass contact member 22 isscrew-threaded and has screwed on to it a dome-shaped electrode 24.Disposed opposite this electrode 24 is a similarly dome-shaped electrode25 screwed into the plate 12. The electrodes 24 and 25 both comprisebrass in this example and define an airgap between them, the width ofwhich is adjustable, to a limited extent, by-- screwing the electrode 24up or down-the contact member 22. r

The electrodes 24 and 25 and the airgap at 26 are enclosed within a tubeof plastics material 27'which extends fromthe bottom of the supportvessel 16 to the plate 12.

Received within the support vessel 16 is a sample container 28 whichcomprises a comparatively thin-walled container, the external shape anddimensions of which correspond to the internal shape and dimensions ofthe support vessel 16. In this example, the container is formed byinjection molding from an acetyl based plastics material which, likethat of the supportvessel 16, may be Delrin (registered trade mark). Inthis exam ple, the wall thickness of the sample container 28 isapproximately Aainches. Secured in the bottom of the container 28 is anelectrode 29. The electrode 29 is secured in position by molding thecontainer 28 around the electrode in situ in the mold. The container 28has an outwardly projecting annular flange 31 at the top for overlyingthe top of the support vessel The container 28 has a lid 32, alsoinjection molded from acetyl based plastics material. The lid 32 isinjection molded around an electrode 33 in situ in the mold. A sealingring 34 is located in an annular groove in the part of the lid 32 whichabuts against the outwardly protruding flange 31 of the sample container28.

A cylindrical brass cap 35 fits over the sample container 28 and isadapted to be pressed into firm contact with the plate 1 1 by a toggleclamp 36. The dimensions of the support vessel 16 and the samplecontainer 28 are arranged so that when the cap 35 is so clamped, the topof the cap 35 applies pressure upon the lid 32 to effect a firm sealbetween the lid 32 and the container 28 and also to make electricalcontact from the plate 11 via the cap 35 to the electrode 33. Thepressure is also transmitted through the sample container 28 to theelectrode 29 to press this into contact with the contact member 22. Itwill be appreciated that the brass cap 35 provides an electrical contactmember for the top electrode 33.

The whole apparatus is enclosed within a box-shaped enclosure 37 havinga hinged lid 37a. A safety device 38 comprises an electricallyconducting rod 39 slidable through an aperture near the edge of plate 11and having a contact member at 41 aligned with a contact member 42 onthe plate 12. A spring 43 biases the rod 39 in a sense tending to bringthe contact members 41 and 42 into contact with one another. With thelid 37a in position on the apparatus, the rod 39 is pressed downwardlyagainst the action of spring 43 so that the contact members 41 and 42are spaced apart. When the lid is opened, the spring 43 moves the rod 39upwardly, bringing the contact members 41 and 42 into contact with oneanother and thereby discharging the capacitors.

' In operation, a sample to be crushed is contained, together with asuitable liquid, usually water, within the sample container 28 clampedin position. The l-LT. supply at 15 is switched on so that thecapacitors 13, 14 begin to charge up. The airgap 26 operates as atriggerable switch which triggers when the voltage appearing across itbecomes high enough for disruptive discharge to occur across the airgap.When this happens, discharge across the electrodes 29 and 33 in theliquid in the sample container 28 is initiated and continues until thecapacitors are discharged to an extent such that the arc dischargeacross the airgap 26 can no longer be maintained. Recharging thencommences and the cycle repeats.

It will be appreciated that the arrangement of this example in which thesample container 28 and airgap 26 are arranged centrally between twoplates 11 and 12 with the capacitors for charging the plates arrangedaround these operative components provides for a low inductance circuit.Cable strap connections are avoided, thus further reducing inductance,while the making of electrical connection between the electrodes 29 and33 with the respective plates 12 and 11 is simply achieved by theclamping operation which also serves to secure and support the samplecontainer. The importance of minimizing inductance is referred to inPatent Specification No. 1,021,786 in which it is explained that fastrise time is an important factor in securing the most rapid crushing tofine particle sizes. Within limits, for a given apparatus, the finer theultimate particle size required, the longer the apparatus will have tobe operated upon the particular sample.

it will be further appreciated that the sample container 28 with its lid32 comprises a scalable enclosure readily removable from or insertableinto the apparatus. Thus a container 28 may be filled with a sample atsome remote location and sealed for subsequent treatment in theapparatus and, if desired, removed to a remote location before unsealingafter crushing has been carried out. Further, as explained above, theremovable sample container 28 and lid 32 does not have to besufficiently robust to withstand explosive forces of theelectrohydraulic crushing. Thus, the container-28 and lid 32 may be madethin enough and small enough to comprise an item which it is reasonabletodispose of after using only once in the apparatus. In this example,the dimensions of the container 28 and lid 32 are chosen so that thecontainer isself-supporting.

An important advantage of this example which provides a disposablesample container is that the risk of cross-contamination from one sampleto the next is avoided or reduced.

The material for the electrodes 33 and 29 is chosen according to theelements which are to be searched for in the sample for analysis andalso depending upon the method in which the sample is to be analyzed.The electrode material must, of course, not comprise hard or brittlematerial likely to be seriously damaged by the electrical discharge. Forexample, where the sample is subsequently to be analyzedspectrographically by introducing the sample into an are between copperelectrodes, then the material selected for the electrodes 29 and 33 ofthe electrohydraulic crusher will be high purity copper. Anothermaterial frequently employed istitani um.

In a modification of the apparatus a slightly different clamping andsafety system has been employed. in the modification an earthed casingencloses all the components below the plate 11.- The clamping system andthe support vessel 16 are accessible on the top of the casing, withouthaving to lift a lid. The clamping system comprises a clamp arm, pivotedon one side of the support vessel to a releasable locking mechanism. Adownwardly extending toothed arm on the end of the clamp arm remote fromthe pivot is engageable in the releasable locking mechanism, which isfixed to the casing. Pressure is applied manually to the clamp arm andis maintained by the engagement of the toothed arm in the releasablelocking mechanism. The releasable locking mechanism can be released onlywith a special key, the releasing movement of which is also operative toearth the lower plate 12. The same key is used for turning on a separateswitch to the high-voltage power supply. The key cannot be removed fromthis switch without turning it off. Thus, the clamp cannot be releasedwithout turning off the power supply and discharging the capacitors.

The invention is not restricted to the details of the forcgoin examples.For instance, the material of the support vessel 16 and sample container28 need not necessarily comprise Delrin (registered trade mark) but mayfor example comprise any other tough, shock-resistant, nonconducting andnoncontaminating material such as, for example, nylon.

We claim:

1. Apparatus for electrohydraulic crushing of samples for analysis,which apparatus comprises support means for supporting a separatelyformed sample container comprising a lid and a body and having spacedelectrodes therein, means for clamping the sample container in thesupport, and means for connecting the electrodes across a high-voltagesource.

2. Apparatus as claimed in claim 1, wherein the support comprises avessel, the internal shape and dimensions of which correspond with theexterior shape and dimensions of the sample container.

3. Apparatus as claimed in claim 2, wherein the clamping means includesa member which overlies the lid of the sample container when positionedin the support vessel, the clamping pressure serving to press the lid ofthe sample container into tightly sealed engagement with the samplecontainer body.

4. Apparatus as claimed in claim 3, wherein the clamping meanssimultaneously serves to press the lid as aforesaid and to Press intoelectrical contact with the said electrodes electrical contact membersconnectable to the high-voltage source.

5. Apparatus as claimed in claim 1, wherein the high-voltage sourceprovides high-voltage pulses and comprises one or more capacitors, meansfor charging the capacitors and means for intermittently discharging thecapacitors through the electrodes of a sample container clamped in theapparatus.

6. Apparatus as claimed in claim 5, wherein the means for intermittentlydischarging the capacitors comprises a gas gap between furtherelectrodes in series with the electrodes of the sample container.

7. Apparatus for electrohydraulic crushing of samples for analysiscomprising opposed rigidly supported electrically conducting plates, oneof which has an aperture therethrough,

one or more capacitors disposed between the plates and electricallyconnected across the plates, a support vessel of electrically insulatingmaterial received in the said aperture and having a flange overlyingpart of the plate, clamping means comprising a member adapted to overliethe lid of a sample container supported in the support vessel, and meansfor pressing the clamping member towards the said apertured plate, anelectrical contact member provided in the support vessel andelectrically connected to the other of the said plates, an electricalcontact member provided by the clamping member, whereby when clampingpressure is applied with a sample con-

1. Apparatus for electrohydraulic crushing of samples for analysis,which apparatus comprises support means for supporting a separatelyformed sample container comprising a lid and a body and having spacedelectrodes therein, means for clamping the sample container in thesupport, and means for connecting the electrodes across a high-voltagesource.
 2. Apparatus as claimed in claim 1, wherein the supportcomprises a vessel, the internal shape and dimensions of whichcorrespond with the exterior shape and dimensions of the samplecontainer.
 3. Apparatus as claimed in claim 2, wherein the clampingmeans includes a member which overlies the lid of the sample containerwhen positioned in the support vessel, the clamping pressure serving topress the lid of the sample container into tightly sealed engagementwith the sample container body.
 4. Apparatus as claimed in claim 3,wherein the clamping means simultaneously serves to press the lid asaforesaid and to press into electrical contact with the said electrodeselectrical contact members connectable to the high-voltage source. 5.Apparatus as claimed in claim 1, wherein the high-voltage sourceprovides high-voltage pulses and comprises one or more capacitors, meansfor charging the capacitors and means for intermittently discharging thecapacitors through the electrodes of a sample container clamped in theapparatus.
 6. Apparatus as claimed in claim 5, wherein the means forintermittently discharging the capacitors comprises a gas gap betweenfurther electrodes in series with the electrodes of the samplecontainer.
 7. Apparatus for electrohydraulic crushing of samples foranalysis comprising opposed rigidly supported electrically conductingplates, one of which has an aperture therethrough, one or morecapacitors disposed between the plates and electrically connected acrossthe plates, a support vessel of electrically insulating materialreceived in the said aperture and having a flange overlying part of theplate, clamping means comprising a member adapted to overlie the lid ofa sample container supported in the support vessel, and means forpressing the clamping member towards the said apertured plate, anelectrical contact member provided in the support vessel andelectrically connected to the other of the said plates, an electricalcontact member provided by the clamping member, whereby when clampingpressure is applied with a sample container supported in the supportvessel, the clamping member applies sealing pressure to the lid of thesample container and electrical contact making pressure betweenelectrodes in the sample container and the respective electrical contactmembers.
 8. A sample container for samples to be electrohydraulicallycrushed prior to analysis, which container comprises electrodes aroundwhich plastics material is molded to form the container.